Backflow valves are forms or assemblies of check or one-way valves, and operate to allow relatively unimpeded flow in one direction through the valve, and to prevent flow through the valve in the reverse or opposite direction. Backflow prevention usually is desirable in order to prevent contamination of the source of fluid which enters the valve from upstream. A valve which is typically employed in or as a back flow valve, includes a flap which is movable between an open position and a closed position. In the open position, the flap allows fluid to flow through the valve, but in the closed position, the flap presses a resilient seal against a valve seat to prevent flow. Valves of this kind can fail and therefore allow flow of fluid through the valve in the reverse direction for example, in circumstances in which corrosion and/or abrasion has caused the seal or valve seat to be damaged, so that a sufficient seal engagement does not occur in the closed flap position. Failure can alternatively occur by way of foreign matter becoming lodged between the seal and the valve seat, and even though the foreign matter may become dislodged by flow of fluid through the valve, permanent damage may have occurred to either the seal or the valve seat so that reverse flow of fluid through the valve continues.
If failure of a backflow valve occurs, the fluid source can be contaminated by additives downstream of the back flow valve, such as acids, detergents, solvents, sewerage, etc. Given the seriousness of contamination, backflow valves typically incorporate a pair of check or one-way valves which are aligned to allow flow therethrough in one direction, but not in the reverse. Two check or one-way valves are provided so that upon failure of one of those valves, the other maintains protection against backflow contamination.
A further feature of one type of backflow valve, is the presence of a relief valve, inserted between the two check or one-way valves. Such a valve is known in the art as a reduced pressure zone valve or assembly. In this arrangement, the assembly operates so that when a first of the check or one-way valves has a sufficient pressure differential, that differential is employed, generally through a diaphragm, to maintain the relief valve closed. As the differential pressure reduces and the diaphragm is unable to maintain the relief valve closed, back flowing fluid is dumped through the relief valve typically to atmosphere. This serves two purposes, the first of which is that the backflowing fluid is prevented from backflowing past the check or one-way valve, and further, personnel are alerted to a potential problem by the fluid being dumped through the relief valve.
The critical nature of backflow valves, is such that many countries have legislative regulations, that require periodic monitoring of such valves to ensure their fail-safe operation. Typically this involves an annual certification process, which requires a skilled operator to connect hydraulic monitoring equipment to the backflow valve and to isolate the valve from the reticulation network. U.S. Pat. No. 5,713,240 (Engelmann), discloses a method that allows certification to be carried out remotely, but the process disclosed by Engelmann requires fluid flow through a pipe containing the valve to have an effective zero flow rate. Also, Engelmann is deficient in being unable to check the proper operation of a backflow valve, when the valve experiences a back pressure, reverse to the normal direction of pressure through the valve. Therefore, while Engelmann discloses an arrangement which does not necessarily require attendance of a skilled operator at the actual backflow valve and which can further test a valve without requiring the pipe to be disconnected from the reticulation network, the disclosed arrangements nevertheless do not allow for monitoring to take place under all circumstances.